Stimuli-responsive polymers. VII. Photomodulated chiroptical switches: Periodic copolyaramides containing azobenzene, phenylene, and chiral binaphthylene main-chain linkages

Conformationally restricted copolyaramides containing a combination of 4,4'-azobenzene, 1,4-phenylene, and chiral 2,2'-binaphthylene main-chain segments exhibit photoresponsive chiroptical behavior stemming from multiple trans-cis-isomerization reactions triggered within their polymer backbones. In contrast to their more randomly constructed counterparts, copolymer variants endowed with periodic backbone structures undergo reversible, wavelength-dependent inversions in their optical rotations in response to multiple ultraviolet-light/visible-light illumination cycles. Similar behavior is also observed for a smaller oligomer fitted with a periodic arrangement of its monomer units. In their present forms, the periodic constructs constitute a new class of solution-based, photomodulated chiroptical switches that may be suitable for applications in a number of emerging technological areas. (C) 2003 Wiley Periodicals, Inc.